For the first time in history, a mammal’s mating behavior without penetration has been documented, specifically in the serotine bat. A study published in Current Biology revealed this fascinating discovery. The male bats’ penises are approximately seven times longer than their female partners and have a heart-shaped head that is seven times wider than the vaginal opening, making penetration impossible. Instead of functioning as a penetration organ, the researchers found that males use their enlarged penises to move the female’s tail sheath away and maintain contact mating.

Nicolas Fasel, lead author of the study from the University of Lausanne, Switzerland, stated, “We think perhaps it is like in dogs where the penis becomes engorged so that it becomes stuck or they simply could not insert it. However, this type of copulation had not been described in mammals until now.”

The study observed genitalia during copulation using camera images placed behind a grate that researchers could climb onto. They analyzed 97 pairings from both the Dutch church and Ukrainian center. The results showed that after copulation, the female’s abdomen appeared moist, suggesting semen was transferred. Further studies are needed to confirm sperm transfer and to deepen our understanding of mating behavior in other bat species.

Researchers also characterized serotine bats’ genitalia by measuring erect penises of live specimens and performing necropsies on those that died. When erect, male serotine bats’ penises are about seven times longer and seven times wider than females’ vaginas of the same species. This study raises new questions about other bat species and highlights never-before-documented mating behavior in mammals.

Overall, this study provides valuable insights into serotine bats’ reproductive practices and highlights new areas for research on bat mating behavior.